Buggy code:
public class UserInterface extends JFrame { private JPanel contentPane ; private JTextField command ; private JTextPane tentativeDisplay ; private JScrollPane tentativeDisplayScrollPane ; private JLabel closeButton ; private JLabel minimiseButton ; private JLabel dragPanel ; private JLabel sectionTitle ; private JLabel sectionTitleLine ; private DisplayPane displayPane ; private int mouseXCoordinate ; private int mouseYCoordinate ; private TaskList currentList ; private boolean isMessageDisplayed ; public static void main ( String [ ] args ) { } public UserInterface ( ) { } private void prepareSectionTitle ( ) { } private void prepareSectionTitleLine ( ) { } private void prepareBackground ( ) { } private void prepareDisplay ( ) { } private long compareList ( TaskList originalList , TaskList modifiedList ) { } private void prepareCommandTextField ( ) { command = new JTextField ( ) ; command . setBounds ( 32 , 433 , 532 , 33 ) ; contentPane . add ( command ) ; command . setColumns ( 10 ) ; command . setBorder ( null ) ; command . setOpaque ( false ) ; command . setFont ( new Font ( "Arial" , Font . BOLD , 20 ) ) ; command . setForeground ( new Color ( 128 , 128 , 128 ) ) ; command . setText ( "Enter<seq2seq4repair_space>commands<seq2seq4repair_space>here" ) ; command . addFocusListener ( new FocusListener ( ) { @ Override public void focusGained ( FocusEvent e ) { command . setForeground ( new Color ( 0 , 0 , 0 ) ) ; if ( isMessageDisplayed ) { command . setText ( "" ) ; isMessageDisplayed = false ; } else { command . setText ( command . getText ( ) ) ; } } @ Override public void focusLost ( FocusEvent e ) { command . setForeground ( new Color ( 128 , 128 , 128 ) ) ; String input = command . getText ( ) ; <START_BUG> if ( ( ! ( isMessageDisplayed ) ) || ( ( input . length ( ) ) <= 0 ) ) { <END_BUG> command . setText ( "Enter<seq2seq4repair_space>commands<seq2seq4repair_space>here" ) ; isMessageDisplayed = true ; } else { command . setText ( input ) ; } } } ) ; command . addKeyListener ( new KeyListener ( ) { @ Override public void keyPressed ( KeyEvent e ) { if ( ( e . getKeyCode ( ) ) == ( KeyEvent . VK_BACK_SPACE ) ) { if ( ( command . getText ( ) . length ( ) ) <= 0 ) { e . consume ( ) ; } } else if ( ( e . getKeyCode ( ) ) == ( KeyEvent . VK_ENTER ) ) { String input = command . getText ( ) ; TaskList tempTaskList ; long newTaskNumber ; if ( ( input . length ( ) ) > 0 ) { Constants . COMMAND_TYPE commandType = Engine . process ( input ) ; tempTaskList = Engine . getAllTasks ( ) ; switch ( commandType ) { case ADD : if ( ( ( tempTaskList . size ( ) ) > ( currentList . size ( ) ) ) && ( ( newTaskNumber = compareList ( currentList , tempTaskList ) ) > 0 ) ) { command . setText ( "Task<seq2seq4repair_space>added<seq2seq4repair_space>successfully" ) ; currentList . copyTaskList ( tempTaskList ) ; displayPane . clearDisplay ( ) ; displayPane . addTasksToDisplay ( currentList ) ; displayPane . selectTask ( newTaskNumber ) ; System . out . println ( ( "line<seq2seq4repair_space>added<seq2seq4repair_space>=<seq2seq4repair_space>" + newTaskNumber ) ) ; } else { command . setText ( "Failed<seq2seq4repair_space>to<seq2seq4repair_space>add<seq2seq4repair_space>task" ) ; } break ; case UPDATE : newTaskNumber = compareList ( currentList , tempTaskList ) ; if ( newTaskNumber > 0 ) { command . setText ( "Task<seq2seq4repair_space>updated<seq2seq4repair_space>successfully" ) ; currentList . copyTaskList ( tempTaskList ) ; displayPane . clearDisplay ( ) ; displayPane . addTasksToDisplay ( currentList ) ; displayPane . selectTask ( newTaskNumber ) ; } else { command . setText ( "Failed<seq2seq4repair_space>to<seq2seq4repair_space>update<seq2seq4repair_space>task" ) ; } break ; case DELETE : if ( ( ( tempTaskList . size ( ) ) < ( currentList . size ( ) ) ) && ( ( newTaskNumber = compareList ( currentList , tempTaskList ) ) > 0 ) ) { command . setText ( "Task<seq2seq4repair_space>deleted<seq2seq4repair_space>successfully" ) ; currentList . copyTaskList ( tempTaskList ) ; displayPane . clearDisplay ( ) ; displayPane . addTasksToDisplay ( currentList ) ; displayPane . selectTask ( ( newTaskNumber - 1 ) ) ; } else { command . setText ( "Failed<seq2seq4repair_space>to<seq2seq4repair_space>delete<seq2seq4repair_space>task" ) ; } break ; case DONE : if ( ( newTaskNumber = compareList ( currentList , tempTaskList ) ) > 0 ) { command . setText ( "Task<seq2seq4repair_space>marked<seq2seq4repair_space>done<seq2seq4repair_space>successfully" ) ; currentList . copyTaskList ( tempTaskList ) ; displayPane . clearDisplay ( ) ; displayPane . addTasksToDisplay ( currentList ) ; displayPane . selectTask ( newTaskNumber ) ; } else { command . setText ( "Fail<seq2seq4repair_space>to<seq2seq4repair_space>mark<seq2seq4repair_space>task<seq2seq4repair_space>as<seq2seq4repair_space>done" ) ; } break ; case INVALID : command . setText ( "Invalid<seq2seq4repair_space>Command" ) ; break ; default : command . setText ( "Feature<seq2seq4repair_space>not<seq2seq4repair_space>supported<seq2seq4repair_space>in<seq2seq4repair_space>V0.1" ) ; break ; } displayPane . requestFocus ( ) ; isMessageDisplayed = true ; } else { e . consume ( ) ; } } } @ Override public void keyTyped ( KeyEvent e ) { } @ Override public void keyReleased ( KeyEvent e ) { } } ) ; } private void prepareTentativeDisplay ( ) { } private void prepareCloseButton ( ) { } private void prepareMinimiseButton ( ) { } private void prepareDragPanel ( ) { } }

Fix:
if ( ( ! ( isMessageDisplayed ) ) && ( ( input . length ( ) ) <= 0 ) ) {